<!doctype html>
<html ng-app="myApp">
<head>
    <meta charset="UTF-8">
    <title>Untitled Document</title>
    <style>
        .menu-disabled-true{
            color: gray;
        }
        
        .menu-disabled-false{
            color: red;
        }
    </style>
    <script type="text/javascript" src="js/angular.js" ></script>
    <script src="angular.min.js"></script>
    <script>
        var myApp = angular.module("myApp",[]);
        myApp.controller("MyController", function($scope){
            $scope.isDisabled = false;
            $scope.changeState = function(){
                $scope.isDisabled = true;
            };
        });
    </script>
</head>
<body ng-controller="MyController">
    <ul>
        <li class="menu-disabled-{{isDisabled}}" ng-click="changeState()">hello</li>
    </ul>
</body>
</html>